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United States Patent |
5,221,952
|
Ishii
,   et al.
|
June 22, 1993
|
Means for separating image recording medium in electrophotographic
recording apparatus
Abstract
An electrophotographic recording apparatus including a light-sensitive drum
for carrying toner images developed thereon, and a transfer unit arranged
at a prescribed distance from the light-sensitive drum for transferring
the toner images from a light-sensitive drum to the image recording paper.
The transfer unit has a charging wire electrode for electrically charging
the paper and a generally inverted U-shaped housing having spaced
sidewalls with respective bottom edges. A separator is provided for
separating the paper from the light-sensitive drum as the paper travels
along a conveying path and comprises a paper separating plate extending
from the downstream one of the bottom edges of the housing of the transfer
unit in the downstream direction of the travel of the paper along the
conveying path side thereof, with and the housing of the transfer unit is
grounded. The paper separating plate has a distal end having a saw tooth
shape along the length thereof, as measured transversely to the conveying
path.
Inventors:
|
Ishii; Masato (Kawasaki, JP);
Tokuhisa; Masanori (Kawasaki, JP);
Kubo; Hirohiko (Hyogo, JP)
|
Assignee:
|
Fujitsu Limited (Kawasaki, JP)
|
Appl. No.:
|
933677 |
Filed:
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August 24, 1992 |
Foreign Application Priority Data
Current U.S. Class: |
399/315; 271/310; 271/900; 399/398 |
Intern'l Class: |
G03G 015/00 |
Field of Search: |
355/315
271/307,310,312,900
|
References Cited
U.S. Patent Documents
4579441 | Apr., 1986 | Hart et al. | 271/900.
|
4699499 | Oct., 1987 | Hoshika et al. | 271/900.
|
4782358 | Nov., 1988 | Shibayama et al. | 355/315.
|
Foreign Patent Documents |
1-235978 | Sep., 1989 | JP | 355/315.
|
Other References
English Abstract of Japanese Kokai 53-104246, Published Nov. 9, 1978.
English Abstract of Japanese Patent Document 2-135385, Published May 24,
1990.
|
Primary Examiner: Moses; R. L.
Attorney, Agent or Firm: Staas & Halsey
Claims
We claim:
1. In an electrophotographic recording apparatus including an image carrier
for carrying toner images developed thereon, means for conveying an image
recording medium to the image carrier in a predetermined direction along a
conveying path, and a transfer unit, displaced by a prescribed distance
from the image carrier for transferring the toner images from the image
carrier to the image recording medium, the transfer unit having means for
electrically charging the image recording medium and further having a
generally inverted U-shaped housing enclosing the charging means and a
pair of spaced sidewalls with respective bottom edges thereof disposed
adjacent the conveying path and accordingly adjacent the surface of an
image recording medium being conveyed along the conveying path, one of the
bottom edges thereof being disposed downstream of the other in the
conveying direction of the image recording medium, a separator which
separates the images recording medium from the image carrier and
comprises:
a metal plate extending from the downstream one of the bottom edges of the
housing of the transfer unit and in the conveying direction of the image
recording medium, the metal plate having a distal and extending along the
length of the metal plate, as measured perpendicularly to the conveying
direction of the image recording medium, the distal end having a saw tooth
shape along the length thereof; and
means for electrically grounding the housing of the transfer unit.
2. A separator according to claim 1, wherein the metal plate has a width,
measured in a direction transverse to the length thereof and thus in a
direction parallel to the conveying direction of the image recording
medium, which is larger than the prescribed distance between the image
carrier and the transfer unit.
3. A separator according to claim 2, wherein the metal plate extends in a
direction generally parallel to the conveying direction of the image
recording medium.
4. A separator according to claim 2, wherein the metal plate is integral
with the downstream one of the bottom edges of the corresponding sidewall
of the outer case of the transfer unit and is bent relatively to the
respective sidewall so as to extend therefrom at an angle.
5. A separator according to claim 1, further comprising insulating members
secured at the distal end of the metal plate and extending substantially.
perpendicularly to the metal plate in a direction toward the conveying
path.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to means for separating an image recording
medium from an image carrier after a transfer of toner images from the
image carrier to the image recording medium in an electrophotographic
recording apparatus.
2. Description of the Related Art
Widespread use of office automation systems requires high quality output
apparatuses in which ordinary paper can be used. For this purpose,
electrophotographic recording apparatuses such as copying machines and
facsimile apparatuses have been realized, and are disclosed, for example,
in Japanese Unexamined Patent Publication (Kokai) No. 53-104246 and No.
2-135385. The electophotographic recording apparatuses include an image
carrier such as a light-sensitive drum carrying toner images developed
thereon, conveying rollers for conveying an image recording medium such as
paper to the image carrier in a predetermined direction for transferring
the toner images from the image carrier to the image recording medium, and
a transfer unit arranged at a specific distance from the image carrier and
having a charging wire electrode causing a corona discharge for
electrically charging the image recording medium. The transfer unit
typically charges the image recording medium to a plus potential to which
minus charged toner on the image carrier is attracted.
In these electrophotographic recording apparatuses, the image recording
medium is brought into contact with the image carrier at a certain contact
portion for transferring the toner images from the image carrier to the
image recording medium and then the image recording medium is disengaged
from the image carrier for directing the image recording medium to a
fixing process. However, the image recording medium is apt to be attracted
to the image carrier after the toner images are transferred from the image
carrier to the image recording medium. Therefore, it is necessary to
separate the image recording medium from the image carrier so that the
transferred images are not disturbed, to obtain high quality products
jamming of the image recording medium does not occur.
To separate the image recording medium from the image carrier, it is known
to provide a DC separating structure comprising a row of deelectrification
needles on the downstream side of the transfer unit as viewed from the
paper conveying direction, the needles being connected to a minus pole of
a power source to pull the plus charged image recording medium and thereby
to separate the image recording medium from the image carrier. However,
the DC separating structure requires a large expenditure for arranging,
for example, a plurality of deelectrification needles.
A curvature separating structure is also known in which the radius of
curvature of the image carrier (light-sensitive drum) is made smaller and
the image recording medium departs from the image carrier at a relatively
large angle between the image recording medium and the tangent line to a
certain point of the image carrier. In this case, however, the available
surface area of the image carrier is small and the limited surface is used
excessively, thereby shortening the life of the image carrier. Further, a
face-up separating structure is also known in which the image recording
medium is conveyed under the image carrier thereby to engage same from
below and thus the separation of the image recording medium from the image
carrier is assisted by the weight of the image recording medium. In this
case, however, there are restrictions in designing the face-up separating
structure rather than the face-down separating structure.
The above described Japanese Unexamined Patent Publication (Kokai) No.
53-104246 and No. 2-135385 also disclose means for separating the image
recording medium from the image carrier. In Kokai No. 53-104246, the means
for separating the image recording medium from the image carrier comprises
a conductive guide roller and a dielectric material covering the
conductive guide roller, with the conductive guide roller being connected
to the ground or a minus pole of a power source. In Kokai No. 2-135385 ,
the means for separating the image recording medium from the image carrier
comprises a conductive guide plate and a dielectric layer sandwiching the
conductive guide plate, with the conductive guide plate being connected to
a minus pole of a power source. It is said that if the conductive guide
roller or plate directly contacts the image recording medium, the
conductive guide roller or plate may disturb the toner images on the image
recording medium and so the dielectric layer is provided to prevent the
conductive guide roller or plate from directly contacting the image
recording medium. In these publications, the means for separating the
image recording medium from the image carrier is provided as a special
component in addition to the transfer unit. Therefore, these means
increase the manufacturing cost of the apparatus.
SUMMARY OF THE INVENTION
The object of the present invention is to provide a means for separating an
image recording medium from an image carrier by which the image recording
medium can be separated from the image carrier with undisturbed images and
can be obtained at a low cost.
According to the present invention, in an electrophotographic recording
apparatus including an image carrier for carrying toner images developed
thereon, means for conveying an image recording medium to the image
carrier in a predetermined direction, and a transfer unit arranged at a
distance between the image carrier and the transfer unit for transferring
the toner images from the image carrier to the image recording medium and
having means electrically charging the image recording medium and a
generally inverted U-shaped outer case with bottoms near the image
recording medium; one of the bottoms being on the downstream side of the
other as viewed from the conveying direction of the image recording
medium, means for separating the image recording medium from the image
carrier and comprising a metal plate extending from one of the bottoms of
the outer case of the transfer unit to the downstream side thereof as
viewed from the conveying direction of the image recording medium; the
metal plate having a length measured perpendicular to the conveying
direction of the image recording medium and a distal end; the distal end
having a saw tooth shape along the length thereof and the outer case of
the transfer unit being grounded.
With this arrangement, the metal plate is integrally connected to the outer
case of the transfer unit and thus is connected to the ground, and the
image recording medium is charged to a plus potential. Accordingly, the
image recording medium is attracted to the metal plate and the image
recording medium is separated from the image carrier. By forming the
distal end of the metal plate in a saw tooth shape, it has been found that
a disturbance of the toner images caused by the metal plate contacting the
image recording medium is considerably mitigated. It is believed that the
metal plate may contact the image recording medium by a portion of the
metal plate near the distal end thereof and an attractive force between
the metal plate and the image recording medium is distributed throughout
the length of the image recording medium, as if points of attractive
forces act were acting on the image recording medium, to thereby prevent
displacement of the toner images and mitigate disturbance of the toner
images.
Preferably, the metal plate has a width, measured parallel to the conveying
direction of the image recording medium; which is larger than the distance
between the image carrier and the transfer unit. Also preferably, the
metal plate extends generally parallel to the image recording medium.
BRIEF DESCRIPTION OF THE DRAWINGS
The present invention will come more apparent from the following
description of the preferred embodiments, with reference to the
accompanying drawings, in which:
FIG. 1 is a diagrammatic side view of an electrophotographic recording
apparatus according to the first embodiment of the present invention;
FIG. 2 is a perspective view of an outer case of a transfer unit of FIG. 1
with a paper separating plate integrally formed with the outer case;
FIG. 3 is a detailed view of the distal end of the paper separating plate;
and
FIG. 4 is a perspective view of an outer case of a transfer unit according
to the second embodiment of the present invention with a paper separating
plate integrally formed with the outer case.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
FIG. 1 shows an electrophotographic recording apparatus, according to the
present invention which comprises a light-sensitive drum 1 as an image
carrier having a light-sensitive surface layer, the electric conductivity
of which changes in response to light, a developing unit 2 for depositing
a toner on the surface of the light-sensitive drum 1 based on a potential
difference between the surface of the light-sensitive drum 1 and toner, an
electric charger 3 for uniformly charging the surface of the
light-sensitive drum 1, an optical system 4 for forming latent images on
the surface of the light-sensitive drum 1 by changing the amount of
charging by laser scanning, a transfer unit 6 for transferring the toner
images from the light-sensitive drum 1 to a paper 5 as an image recording
medium, and a fixing unit 7 having a halogen lamp or the like to heat and
fix the toner images on the paper 5. The paper 5 is conveyed to the
light-sensitive drum 1 at the position of the transfer unit 6, and further
to the fixing unit 7, in the direction of the arrow by pairs of conveying
rollers 14 and 15.
The transfer unit 6, is arranged above the light-sensitive drum 1 at a
specific distance from the light-sensitive drum 1. The transfer unit 6 has
a charging wire electrode 8 causing a corona discharge for electrically
charging the paper 5 to a plus potential and whereby the minus charged
toner is attracted to the paper 5. The transfer unit 6 also has a spaced
sidewalls with respective bottom edges generally U-shaped outer case 9, or
housing with 9x and 9y near the path of travel of the paper 5 which
encloses the charging wire electrode 8. The bottom edge 9x is on the
downstream side of the other bottom edge 9y as viewed from the conveying
direction of the paper 5. The outer case 9 is made from metal and
connected to a ground as shown.
As shown in FIGS. 1 and 2, a paper separating plate 10 extends from the
bottom 9x to the downstream side thereof as viewed from the paper
conveying direction. In the embodiment, the paper separating plate 10 is
an integral portion of the outer case 9, bent from the vertical sidewall
at the bottom edge 9x. However, it is possible to make the paper
separating plate 10 separately from the outer case 9 and then attach the
paper separating plate 10 to the outer case 9.
As shown in FIG. 3, the paper separating plate 10 has a length L, measured
perpendicularly to the paper conveying direction, and a distal end that is
remote from the bottom 9x of the outer case 9. The distal end has a saw
tooth shape defined by teeth 10a along the length L thereof. The length L
is typically 259 millimeters, and a pitch P between the adjacent teeth is
2 millimeters. The height H of each tooth is 2.4 millimeters and the top
and the valley of each tooth are rounded.
Also, the paper separating plate 10 has a width W, measured in a direction
parallel to the paper conveying direction; the width W (larger than 2
millimeters, for example) being larger than the distance (smaller than 2
millimeters, for example) between the light-sensitive drum 1 and the
transfer unit 6, as shown in FIG. 1. The paper separating plate 10 extends
generally parallel to the paper 5, and preferably, the paper separating
plate 10 is slightly inclined relatively to the paper 5 on the downstream
side of the light-sensitive drum 1 so that the distal end of the paper
separating plate 10 is close to the paper 5.
In operation, latent images are formed on the light-sensitive drum 1 by the
optical system 4, and the toner is adhered to the light-sensitive drum 1
to form toner images thereon at the developing unit 2, as is well known.
Then the toner images are transferred from the light-sensitive drum 1 to
the paper 5.
The paper separating plate 10 is connected to the ground, and the paper 5
is charged to a plus potential, whereby the paper 5 is attracted to the
paper separating plate 10 and thus separated from the light-sensitive drum
1. Since the distal end of paper separating plate 10 is in a saw tooth
shape, it has been found that a disturbance of the toner images caused by
the paper separating plate 10 contacting the paper 5 is considerably
mitigated. It is believed that an attractive force between the paper
separating plate 10 and the paper 5 is distributed throughout the length
of the paper 5 as if points of attractive forces act on the paper 5 to
thereby prevent displacement of the toner images and mitigate disturbance
of the toner images.
FIG. 4 shows an outer case 9 of a transfer unit 6 according to the second
embodiment of the present invention with a paper separating plate 10
integrally formed with the outer case 9. The transfer unit 6 can be
arranged in an electrophotographic apparatus in FIG. 1. In this
embodiment, the paper separating plate 10 has a distal end having a saw
tooth shape 10a along the length thereof and insulating members 11 are
secured at the distal end of the paper separating plate 10. This
arrangement prevents the paper 5 from electrically contacting the paper
separating plate 10 to thereby prevent a concentration of forces
attracting the paper 5, to thereby prevent displacement of the toner
images and mitigate disturbance of the toner images.
As explained above, it is possible, according to the present invention, to
obtain a means for separating an image recording medium from an image
carrier by which the image recording medium can be separated from the
image carrier with the images undisturbed and can be obtained at a low
cost.
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